1. Field
The present invention relates to a secondary battery of an improved electrical structure, and more particularly, to a secondary battery in which the structure of a lead connected to a tab is adaptively improved to enhance the electrical characteristics and performance of the secondary battery in a high capacity environment.
2. Description of Related Art
Secondary batteries have high applicability depending on the product group and excellent electrical characteristics such as high energy density, and thus are commonly used as electric power sources of electric vehicles (EVs) and hybrid vehicles (HVs) as well as mobile devices.
These secondary batteries can radically decrease the use of fossil fuels and also have the advantage of not generating any by-products that come with energy consumption. For these reasons, secondary batteries improve energy efficiency, are environmentally friendly, and are gaining attention as a new alternative energy source.
Secondary batteries (cells) may be classified into pouch-type batteries, cylindrical batteries, prismatic batteries, and the like, based on the type or structure of a casing. Also, secondary batteries may be sorted into jelly-roll (winding) type batteries, stack type batteries, stack/folding type batteries, and the like, based on the structural characteristics of an electrode assembly. Since these types of batteries have corresponding basic principles and configurations, a structure of a secondary battery is briefly described below with reference to FIGS. 1 to 4 illustrating pouch-type secondary batteries.
Referring to FIG. 1, a pouch-type secondary battery 10 basically includes a pouch-shaped battery casing 20 and an electrode assembly 30, also called an electrode current collector.
The electrode assembly 30 includes a cathode plate 3, an anode plate 5, and a separator 4 interposed therebetween to electrically insulate the cathode plate 3 from the anode plate 5, as shown in FIG. 2.
The cathode plate 3 has a cathode tab 32 formed on at least one area of the cathode plate 3, and the anode plate 5 has an anode tab 34 formed on at least one area of the anode plate 5. As shown in FIG. 3, at least one cathode tab 32 and at least one anode tab 34 are converged in a predetermined direction and coupled to a conductive cathode lead 36 and a conductive anode lead 38, respectively, for example, by resistance welding, ultrasonic welding, laser welding, rivets, and the like.
By coupling to the electrode tabs 32 and 34, the electrode leads 36 and 38 serve as a predetermined electrode interface to electrically connect the secondary battery 10 to external devices.
As shown in FIG. 4, the secondary battery 10 may include a plurality of the cathode tabs 32 and the anode tabs 34 having different directions, and in this instance, the number of the electrode leads 36 and 38 electrically connected to the electrode tabs 32 and 34 corresponds to the number of the electrode tabs 32 and 34.
The electrode assembly 30 is mounted in an inner space 23 of the pouch-shaped casing 20 as shown in FIG. 1, and subsequently, an electrolyte is injected, followed by post-processing such as sealing, aging, forming, and the like, resulting in a secondary cell.
Although FIG. 1 shows the two-part pouch-shaped casing 20 of an upper casing 21 and a lower casing 22 divided based on the relative location and the receiving space 23 formed in both of the casings 21 and 22 to receive the electrode assembly 30 therein, the present invention is not limited in this regard.
It is obvious to a person having ordinary skill in the art that a variety of combinations or modifications may be made to a casing, for example, an integrated casing or a two-part casing, or to a space for receiving an electrode assembly, depending on the raw material of the casing, properties or specification of a product, processing conditions, and the like.
An individual secondary battery is referred to as a cell, and a group of secondary batteries is referred to as a battery assembly or a battery pack. Unless otherwise mentioned in the present specification, a secondary battery is defined not only as a cell, but also as a battery assembly or a battery pack.
Recently, as secondary batteries are needed and used in a high capacity environment for HVs, EVs, or for energy storage, the size and capacity of secondary batteries is also increasing
However, since secondary batteries are repetitively charged/discharged by electrochemical reactions, the heat generated during charge/discharge dramatically increases with increasing battery capacity. The heat generation may fatally deteriorate the performance of secondary batteries allowing electrochemical reactions.
To adapt to the high capacity condition of secondary batteries, increasing the number or the size of tabs and leads has been used. However, simply increasing the physical environment of tabs and leads does not achieve a stable and reliable joint between the tabs and the leads.
Moreover, as the number of tabs and leads increases, the number of joints therebetween increases. In the case the number of joints between different physical elements such as above increases, the manufacturing process becomes more complex and a non-uniform electrical characteristic such as an electrical resistance may result, which may be a significant hindering factor in continuously maintaining the normal performance of secondary batteries.
The non-uniform resistance leads to local or partial heat generation or side reactions. The local or partial heat generation may hinder the uniform performance and accelerate the degradation rate of secondary batteries.
Also, simply enlarging an electrode structure to improve the resistance characteristics may cause a short circuit between electrodes when swelling occurs or external physical impacts are applied. Accordingly, there is a need to generally and comprehensively solve the foregoing problems in consideration of high capacity environment where secondary batteries may be placed.